Zenoviy Kohut

In this work, the elastic properties of Rb2SO4 crystals at room temperature were investigated. A pronounced elastic anisotropy was revealed (with maximum stiffness along the Y-axis), as well as differences among the elastic constants, indicating a complex nature of interatomic forces due to the presence of rigid [SO4]2− tetrahedral groups. The importance of taking into account the influence of the polarizability of rubidium ions (Rb+) and [SO4]2- groups, which possess large electron shells that deform under mechanical compression of the crystal, was noted. The spatial distributions of the Young’s modulus, bulk modulus, shear modulus, and Poisson’s ratio were calculated within the Voigt, Reuss, and Hill approximations. The degree of anisotropy of the elastic properties of the Rb2SO4 crystal was evaluated (AU = 0.405). The eigenvalues λi of the stiffness matrix, which are of key importance for determining the physical stability of the crystal, were calculated.

The elastic stiffness coefficients of K2SO4 crystals at room temperature were calculated. The coefficient C66 is the smallest among the diagonal components, indicating a “soft” shear mode in the XY plane. The Born stability criteria were evaluated, and their fulfillment confirms the thermodynamic stability of the crystal. The Cauchy relations were also analyzed. The spatial distributions of Young’s modulus and Poisson’s ratio of K2SO4 crystals were constructed. The Young’s modulus surface is close to spherical in shape (a “rounded parallelepiped”) with pronounced protrusions along the [010] and [001] crystallographic directions. The values of Poisson’s ratio (within 0.23–0.27) are typical for ionic-covalent crystals of intermediate stiffness, indicating moderate transverse deformation. The elasto-optic parameters of K2SO4 crystals were analyzed. The baric (pressure-induced) changes in the refractive indices were calculated. It is shown that the temperature variation of the refractive index (dni/dT) in these crystals is governed by a complex interplay between volumetric and structural factors. The contributions to the temperature-induced refractive index changes arising from variations in atomic polarizability (≈ 32%) and crystal density (≈ 68%) were estimated.

A simply supported rectangular isotropic ferromagnetic plate with magnetocaloric properties subjected to convective heating on its upper surface is considered. The governing equations comprise a system of two-dimensional transient equations for the thickness-averaged temperature characteristics of the plate and the two-dimensional bending equations for isotropic plates expressed in terms of generalized displacements within the framework of first-order shear deformation theory. Closed-form solutions to the governing equations are obtained by expanding all thermal and mechanical field quantities in double Fourier sine series satisfying the prescribed boundary conditions, combined with the Laplace transform in time applied to the thermal quantities. A comparative numerical analysis is carried out for the magnetocaloric ferromagnetic plate and a carbon steel plate under ambient temperature rising at a finite rate to a prescribed value. The dependences of all quantities under investigation on the ambient temperature rise rate, time, convective heat transfer coefficient, thermal conductivity of the ferromagnetic material, and geometric parameters of the plate are analyzed and presented graphically. The results obtained provide a quantitative basis for assessing the thermoelastic state and for optimizing the geometry and operating conditions of active magnetic regenerator plate stacks with a view to enhancing their structural reliability.

A physical and mathematical model is proposed that takes into account the sequential interaction of electromagnetic, temperature, and mechanical fields to assess the thermostressed state of an electroconductive body and predict its load-bearing capacity under the action of an external non-stationary electromagnetic field. Initial-boundary problems are formulated to determine the parameters of the electromagnetic field, temperature, dynamic thermoelastic stresses, and their intensities in a long, solid, non-ferromagnetic electroconductive cylinder. Based on the Huber–von Mises criterion, an assessment of the load-bearing capacity of this cylinder is proposed. A numerical analysis of Joule heat, ponderomotive force, temperature, components of the dynamic stress tensor, and their intensities in a solid stainless-steel cylinder under the action of an amplitude-modulated radio pulse is performed. The limiting values of the amplitude–frequency characteristics and the duration of the electromagnetic action, at which the cylinder under consideration retains its load-bearing capacity as a structural element, have been established.

A physical and mathematical model and a methodology for studying the mechanical properties of a nonferromagnetic conductive panel under the action of a quasi-steady electromagnetic field are proposed. A two-dimensional thermomechanics problem is formulated for the considered panel of a rectangular cross-section. The initial relations for finding the determinant functions, namely, the components of the quasi-static stress tensor, are given. The thermomechanical problem was addressed using the author’s approach, which involves approximating the defining functions by cubic polynomials along the thickness direction. This approach enabled the transformation of the initial two-dimensional boundary value problems into one-dimensional formulations based on the integral characteristics of the defining functions. Using a finite integral transformation in the transverse coordinate, the expressions of all integral characteristics and determinant functions were obtained. On the basis of the proposed mathematical model, a computer analysis of all components of the quasi-static stress tensor and stress intensity in a tungsten panel depending on the dimensionless Fourier time, the Biot criterion, and the induction heating parameters was carried out. The thermomechanical behavior of the panel was analyzed using two modes of near-surface and in-depth induction heating of the panel by a homogeneous quasi-steady electromagnetic field.

This article presents the technology for the preparation of a nitrogen-containing nanoporous bio-carbon and investigates its properties. It has been shown that the synthesised bio-carbon is characterised by a high degree of homogeneity, which has been confirmed by energy dispersive spectroscopy. The obtained bio-carbon has a micromesoporous structure, which has been confirmed by the results of studies using the method of low-temperature nitrogen adsorption and desorption. It was found that the specific surface area of biochar is 1247 m²/g. The data on nitrogen adsorption and desorption were compared with the data on small-angle X-ray scattering, and it was found that the micropores in the synthesised bio-carbon are open pores, while mesopores remain closed. The energy dispersion analysis showed that the structure of the bio-carbon does not contain ferromagnetic atoms, but due to the addition of nitrogen, the synthesised bio-carbon in a magnetic field has the properties of a ferromagnet with a characteristic hysteresis of the specific magnetisation. It was found that this material has a saturation magnetisation σ_s of 1.4 A∙m²∙kg⁻¹ and a coercive force H_c of 10 kA/m. Symmetric supercapacitors were fabricated from the synthesised bio-carbon material with 30% aqueous KOH and 1 M Na₂SO₄ as electrolytes. It was found that for bio-carbon synthesised at 800 °C, the specific capacitance in a 30% aqueous solution of KOH is 180 F/g, and in a 1 M aqueous solution of Na₂SO₄, it is 124 F/g. The cyclic voltammetry of the fabricated supercapacitors at different rates of potential expansion was investigated and analysed. Impedance studies on these supercapacitors were carried out. The equivalent electrical circuits describing the electrochemical processes in the studied supercapacitors were constructed and characterised.

W artykule przedstawiono sposób wykorzystania akumulatorów w domu jednorodzinnym, podłączonym do systemu fotowoltaicznego. Dokonano analizy wpływu pojemności akumulatorów na współczynnik samowystarczalności oraz bilans energetyczny w okresie rocznym. Omówiono wyniki symulacji przepływu energii elektrycznej w hybrydowym systemie fotowoltaicznym przeznaczonym do domu jednorodzinnego.

The article presents a technology for producing nitrogen-containing nanoporous biocarbon with high degree of elemental composition homogeneity, confirmed by electron spectroscopy. The research explores the relationship among the electronic characteristics of supramolecular nanoporous carbon, its porous structure, and the capacitance at its interface with the electrolyte. The obtained biocarbon is characterized by micro and mesopores, as evidenced by the results of studies by the method of nitrogen adsorption/desorption. The specific area of the available porous surface was found to be 1247 m2/g. Comparing this result with the data of small-angle X-ray scattering, we conclude that micropores are open while mesopores remain closed. This material was found to have a saturation magnetization σs of 1.4 A∙m2∙kg-1 and a coercive force Hc of 10 kA/m. The impedance studies of electrochemical cells of supercapacitors made of the experimental biocarbon were carried out. Equivalent electrical circuits of the studied electrochemical processes were constructed and characterized.

W artykule przeanalizowano aktualny stan badań eksperymentalnych i symulacji elementów słonecznych (ES) opartych na CuInxGa1-xSe2 (CIGS) oraz omówiono sposoby zwiększenia efektywności. Podano wyniki symulacji ogniw słonecznych opartej na CIGS w programie SCAPS-1D. Wprowadzenie różnego rodzaju defektów oraz dodatkowego materiału warstwowego pozwoliło uzyskać wysokie wartości cech ES.